During operation of an internal combustion engine, it is desirable to control the formation and emission of certain gases, such as the oxides of nitrogen (NO.sub.x). In particular, NO.sub.x is produced when nitrogen and oxygen are combined at very high peak temperatures within the main combustion chamber of the engine. Such high peak temperatures facilitate the oxidation or "burning" of nitrogen with oxygen, both of which are part of the air present in the main combustion chamber. The amount of NO.sub.x which is formed increases as the peak combustion temperatures within the main combustion chamber increases.
Hence, a number of "lean-burn" internal combustion engines have heretofore been designed in order to reduce the amount of NO.sub.x produced during operation thereof. A lean-burn internal combustion engine utilizes a lean gaseous fuel mixture which has a relatively large air-to-fuel ratio (i.e. having significantly more air) when compared to a gaseous fuel mixture having a stoichiometric air-to-fuel ratio. Use of such lean gaseous mixtures reduces the peak combustion temperatures thereby reducing the amount of NO.sub.x which is produced during operation of the internal combustion engine.
Because of the lean air-to-fuel ratio, it is often difficult to consistently achieve complete and thorough combustion within the main combustion chamber of the internal combustion engine, especially in large bore engines, due to the relatively slow rate of flame propagation from a single point ignition source such as a spark plug. Moreover, turbulence within the main combustion chamber may disadvantageously extinguish the ignition flame that is propagating through the cylinder prior to complete combustion of the lean gaseous fuel therein. When the ignition flame is extinguished in such a manner, the power output of the engine is disadvantageously reduced. In addition, the amount of raw, uncombusted fuel which is exhausted from the engine is disadvantageously increased.
To this end, a number of internal combustion engines have heretofore been designed which have a fuel combustion assembly which includes a precombustion chamber. A precombustion chamber is a relatively small gas accumulating chamber which is positioned in the engine head so as to be in fluid communication with the main combustion chamber of the engine via a number of small orifices. An enriched gaseous fuel is advanced into the precombustion chamber. A spark plug associated with the engine ignites the enriched gaseous fuel within the precombustion chamber (as opposed to igniting the lean gaseous fuel in the main combustion chamber). Ignition of the enriched gaseous fuel creates a front of burning fuel which is jetted or otherwise advanced through the orifices and into the main combustion chamber thereby igniting the lean gaseous fuel therein. The front of burning fuel jetting out of the orifices is generally a sufficient ignition source to cause complete combustion of the lean gaseous fuel within the main combustion chamber without being extinguished by the turbulence therein.
However, use of precombustion chambers which have heretofore been designed has a number drawbacks associated therewith. For example, the internal combustion engine must be configured to include an enriched fuel source, along with a fuel delivery system, for advancing enriched gaseous fuel into the precombustion chamber. Such a configuration increases the number of components associated with the internal combustion engine thereby disadvantageously increasing costs associated with the engine. In addition, although use of lean gaseous fuels reduces the amount of NO.sub.x produced in the main combustion chamber, an undesirable amount of NO.sub.x is produced in the precombustion chamber due to the combustion of enriched gaseous fuels therein.
What is needed therefore is a fuel combustion assembly for an internal combustion engine which overcomes one or more of the above-mentioned drawbacks.